This invention relates to a transmission system having three differentials for use in a four-wheel drive vehicle, and particularly for use in a vehicle having a transverse power-drive unit, that is, a unit arranged perpendicular to the longitudinal direction of the vehicle.
French patent application FR-82 08 440 filed May 14, 1982 discloses a tranmission system comprising a first differential, the input member of which being driven from the output shaft of a gear box, and of which the two output members are connected to one of the front wheels and to the input member of a second differential, the two output members of which being connected to the second front wheel and to a transmission shaft which is itself connected to a differential associated with the rear wheels.
Such an arrangement entails a drawback in that the two front wheels are not driven from the same differential and this can cause a drive dissymetry.
There are also known arrangements in which a central differential has its two output members connected to two other differentials, the central differential and the differential associated with the front wheels being arranged coaxially approximately between the two front wheels, so that one of the transmission shafts of the front wheels extends through the central differential.
Such known arrangements (GB-A-2074 517-JP-A-58/63523) are bulky and adaptation of these arrangements to standard or production line vehicles is difficult.